The invention relates generally to the copying of originals of photosensitive material, especially photographic originals.
More particularly, the invention relates to a method of positioning coherent originals of a strip of photosensitive material in a copy window of a copying apparatus having automatic conveying means for the photosensitive material. The conveying means is controlled by a photoelectric unit which detects the edges of the originals.
The invention also relates to a copying apparatus which allows coherent originals of a strip of photosensitive material to be properly positioned in a copy window of the apparatus. The apparatus includes the previously mentioned automatic conveying means and photoelectric unit, and the latter has a scanning slit which is in register with, and extends transverse to, the path defined by the conveying means. The apparatus further includes a memory which stores the signals from the photo-electric unit in correlation to the position coordinates of the respective regions of the photo-sensitive material responsible for the signals. A processing unit is provided to calculate position coordinates for the originals based upon the signals obtained from the scanning of a section of the photosensitive material containing several originals.
A method of and a device for automatically detecting the image areas of a filmstrip by photosensitive scanning is known from the West German Pat. No. 27 05 097, for example. Scanning is accomplished via an illuminated scanning slit which extends parallel to the separating bands between neighboring image areas and is moved relative to the film. Here, the distance between leading and trailing edges of the images is newly determined for each film, e.g., on the basis of the density values measured within the confines of the slit, and this distance used to find poorly defined image edges when the remaining image edges are readily detectable. In the apparatus described in the West German patent, a gap equivalent to the length of several negatives or originals lies between the scanning slit and the processing station where an edge notch is applied in correlation to a detected image. Within this gap, a pattern containing an integral multiple of the measured total length of an original plus separating band is placed over the scanned film in order that even less readily detectable image edges can be located.
A problem arises in precisely following a region of the film which becomes established as the location of an image edge on the basis of subsequent calculations during travel from the scanning station to the processing station. The distance measurement involved is normally carried out by means of friction rolls engaging the film and arranged so that the rotational movement thereof is converted into pulses or, when a stepping motor is employed for film transport, by counting the control pulses for the motor. The precision of this distance measurement depends upon the absence of slip between the film surface and the measuring or drive rolls, and upon the absence of wear which would change the diameter of the friction rolls. However, these two requirements are very difficult to satisfy simultaneously. As a rule, rolls having a high coefficient of friction are subject to wear and can deform elastically. On the other hand, wear-resistant rolls have a smooth surface so that slip occurs readily. The precision with which film transport is monitored is thus critical, especially when movement of the film is to be monitored over relatively large distances.